1. Field of the Invention
This invention relates to a novel, plastic-filled, lubricated wire rope and to a method of its manufacture.
2. Related Art
Many attempts have been made to impregnate wire rope with plastic materials in order to decrease wear and fatigue of the rope and increase its life. For example, Canadian Pat. No. 582,779 issued Sept. 8, 1959 to Robert E. Campbell describes a vacuum impregnation of wire ropes with an elastomeric plastic material which is subsequently caused to undergo setting or gelation within the rope. Also, Canadian Pat. No. 716,845 issued Aug. 31, 1965 to Alfred Dietz describes a standard wire rope wherein synthetic plastic material is worked into the natural gaps in such a manner that it engages laterally in the gaps between the wires of the outer strands.
Furthermore, Canadian Pat. No. 1,007,526 issued Mar. 29, 1977 to Peter P. Riggs, describes a method of impregnating lubricated wire rope with a thermoplastic material wherein the rope is first formed while coating the strands with a heavy viscous lubricant, then the lubricated rope is preheated to a temperature in the range of about 38.degree. C. to 134.degree. C., then the outer strands of the wire rope are held spaced apart from one another and while the strands are so spaced, the rope is impregnated with a plastic composition so as to entrap the lubricant in the core and the strands.
All the above methods, and the resulting ropes, have certain inherent disadvantages which render them unsatisfactory. The Campbell patent requires working under a vacuum with ropes which must first be degreased and carefully prepared. The Dietz patent will not achieve a very good anchoring of the plastic rope because the plastic does not penetrate into the strands themselves. Such rope would, therefore, not be suitable for severe working environments for use, e.g. as a shovel rope which is subjected to a lot of bending and abuse.
Finally, the Riggs patent requires a special arrangement to hold the outer strands of the wire rope spaced from one another while the plastic material is incorporated. Also, since the lubricant is entrapped, the plastic material cannot fully penetrate the rope and strands and is much more likely to peel off in bending under heavy use. However, the retention of the lubricant within the rope is not the easiest of tasks to perform since the plastic material will sometimes tear or crack, thus enabling the lubricant to escape, thereby weakening the rope in that place.